The present invention relates to a disc drive microactuator system and more particularly to an improved structure for reduced mass of the microactuator rotor.
The density of concentric data tracks on magnetic discs continues to increase (that is, the width of data tracks and radial spacing between data tracks are decreasing), requiring more precise radial positioning of the transducing head. Conventionally, head positioning is accomplished by operating an actuator arm with a large-scale actuation motor, such as a voice coil motor (VCM), to radially position a slider (which carries the head) on a gimbal at the end of the actuator arm. The large-scale motor lacks sufficient resolution to effectively accommodate high track-density discs. Thus, a high resolution head positioning mechanism, or microactuator, is necessary to accommodate the more densely spaced tracks.
One particular design for high resolution head positioning involves employing a high resolution microactuator in addition to the conventional lower resolution actuator motor, thereby affecting head positioning through dual-stage actuation. Various microactuator designs have been considered to accomplish high resolution head positioning. Microactuators typically include a stator portion and a rotor portion, the stator being attached to the gimbal and the rotor supporting the slider. The rotor is movable with respect to the stator such that the slider can be precisely positioned over a track of a disc.
To accomplish fine positioning of the microactuator, a magnetic circuit allows the rotor to be moved in response to a current provided to the magnetic circuit. The magnetic circuit comprises a bottom keeper, magnets, a conductive coil, and a top keeper. The magnetic circuit generates a microactuator force to allow movement of the rotor in response to the current and the microactuator force is typically constant. Prior art microactuator configurations place a substantial amount of heavy magnetic circuit components on the rotor.
The microactuator has suspension springs which can be arranged to provide linear motion of the slider by the microactuator. A disadvantage of linear microactuators is the inability to control large amplitude oscillation of the rotor caused by VCM actuator seeking. During seek acceleration of the VCM to coarsely position the actuator arm, the entire microactuator is in linear motion and large amplitude ringing occurs. The acceleration force of the VCM causes the suspension springs in the microactuator to oscillate the rotor carrying the slider within the stator at a resonant frequency causing the large amplitude ringing. Controlling the large amplitude oscillation of the rotor can be done by predisplacing the rotor to the position it would have during steady state VCM acceleration. For example, predisplacing the rotor may be accomplished by applying a current to the microactuator which generates a microactuator force sufficient to oppose the VCM acceleration force and reduce the net force exerted on the rotor. The microactuator force generated by the magnetic circuit to predisplace the rotor is a function of VCM acceleration and rotor mass.
A high VCM acceleration is desirable to reduce the track seeking time and increase the data throughput of the drive. If the microactuator force remains constant during disc drive operation (as it typically does), the ability to increase the VCM acceleration requires reducing the mass of the rotor. There exists a need in the art for a microactuator having a reduced rotor mass.
The present invention relates to a disc drive having a disc rotatable about an axis, a slider carrying a transducing head for transducing data with a disc, and a dual stage actuation assembly supporting the slider to position the transducing head adjacent a selected radial track of the disc. The dual stage actuation assembly includes a movable actuator arm and a suspension assembly supported by the actuator arm wherein the suspension assembly includes a gimbal. The disc drive actuation assembly further includes a microactuator. The microactuator includes a stator having a top surface and a bottom surface wherein the gimbal is connected to the top surface of the stator. A rotor is operatively connected to the stator and the rotor supports the slider. A magnetic keeper structure is supported by the stator such that the rotor moves with respect to the magnetic keeper structure.